Establishing and verifying the structural integrity of components and structures is important in many industries, such as aviation, automobiles, petroleum, and construction. Loss of structural integrity can be caused by material defects, such as disbonds, delaminations, cracks, corrosion, embedded contaminants, inclusions, and voids that can exist in a composite or monolithic component or structure. For example, it is important in the aviation industry that reliable nondestructive inspection (NDI) techniques exist to examine the structural integrity of each aircraft's fuselage and other structural components to assure that the aircraft will not experience structural failure during operation. Point-by-point inspection of airplanes may thus be advisable, and may be required to be performed, at routine service intervals. Similarly, by way of example, non-invasive inspection and analysis of automotive components such as load-bearing panels, and of petroleum and other chemical transport pipelines, can be of value in the detection of minor flaws, allowing them to be repaired and preventing them from growing into potentially harmful ruptures.
One current method for non-invasive analysis of materials and/or components for defects includes treating the material or component with a dye penetrant such that the dye enters any crack or defect that may exist. The component is then cleaned and then treated with a powder that causes the dye remaining in the defects to wick into powder. Next, ultraviolet light is applied to the material or component causing the residual dye remaining in any cracks or defects to fluoresce. This technique has drawbacks however. The dye sometimes is not suitable to identify cracks that located in areas other than the surface of the component. In addition, this technique is can be operator dependent in that the person performing this technique should be adequately trained and skilled.
Other methods currently utilized for the non-invasive analysis and inspection of materials and components include use of an electromagnetic current and use of thermal imaging including ultrasonic excitation or ultrasonic thermography.
The non-invasive analysis method of using an electromagnetic current is carried out by employing an electromagnetic coil to induce eddy currents in the test material or component. The current pattern changes at the location of a defect or crack. This technique requires point by point inspection, which can be labor intensive and is to some extent limited to only specific types of defects. In addition, the evaluator must be properly trained and skilled.
Ultrasonic thermography is a non-invasive analysis method by which a component, material, or structure, or a portion thereof, is excited with an ultrasonic pulse using an ultrasonic transducer pressed against the surface of the test subject. The resulting mechanical vibration of the subject under test tends to feature differential motion across the face of any defects that may be present, producing friction and causing the defects to heat up sharply, while defect-free areas of the test subject tend to be only minimally and uniformly heated by the vibration. Heat diffusing to the surface from a defect within the volume of a test subject causes a transient local surface temperature increase that can be detected as a bright spot in an image captured shortly after the ultrasonic pulse using, for example, an infrared camera. This ultrasonic thermography technique can identify disbonds, delaminations, cracks, corrosion, embedded contaminants, inclusions, voids, and other types of defects within a broad range of metallic, fiber reinforced plastic, composite, and other structural materials used in the transportation, construction, and other manufacturing industries. It is to be understood that finding defects is not the same as correcting them; ultrasonic thermography as applied herein is primarily a tool for detection.
Ultrasonic thermography has proven successful for detecting defects in materials and components in research, production, and operational maintenance environments. Some presently available analysis systems employing ultrasonic thermography techniques have drawbacks and limitations, however. For example, some presently available ultrasonic thermography systems can analyze only small specimens, and are generally restricted to laboratory use. Some other such systems require manual placement, orientation, and application of force between the transducer and the test surface, which requirements can degrade the repeatability, accuracy, and noninvasive nature of the technique. That is, too much or too little pressure applied to the transducer during a pulse may degrade the repeatability of detection, while misalignment of the transducer can cause the part or surface being inspected to be cut or burned, or can cause damage to surface finishes. Such systems are thus not always well suited for field inspection of materials or components, or for inspection of large objects, such as fuselages and flight control structures of in-service airplanes.
Accordingly, it is desirable to provide an apparatus and method for detecting defects of multiple types in both metal and composite structures. It is also desirable to provide an apparatus and method for effectuating the quick and efficient inspection and analysis of large components and/or large amounts of materials, such as entire airplane fuselages and structures, in real time. It is further desirable to provide a repeatable analysis apparatus and method using ultrasonic thermography to effectuate inspection of large components or areas to detect disbonds, delaminations, cracks, corrosion, embedded contaminants, inclusions, voids, and other defect types. It is desirable as well that an ultrasonic thermography apparatus should be readily transportable, usable under field as well as laboratory conditions, and usable by a small team of operators.